1. Field of the Invention
This invention relates to underwater couplings for joining sections of tubular goods. More particularly, it relates to underwater couplings for conduits used for electrical or fiber optic cables.
2. Description of the Related Art
Offshore petroleum exploration and production is an increasingly important part of the energy industry. As the sophistication of the process grows, there is an increasing need for data communication and the exchange of control signals between surface facilities (e.g., a drilling platform or a production platform) and equipment on the ocean floor or within the well bore. So-called “smart wells” have sensors within the well and/or well head which send data relating to the status of the well to the operator monitoring the well's performance. Hydraulic lines are often used for control purposes. Electrical cables are typically used to transmit data. However, in the marine environment, a leak in an electrical cable almost always results in a short circuit due to the high conductivity of sea water. Accordingly, data transmission using fiber optic cables offers a significant advantage. A fiber-optic system is similar to the copper wire system that it replaces. The difference is that fiber-optics use light pulses to transmit information over thin strands of glass (“fibers”) instead of using electronic pulses to transmit information through copper lines. Fiber-optic based systems offer advantages in: speed; bandwidth; the distance signals can be transmitted without needing to be “refreshed” or amplified; resistance to electromagnetic noise; and, maintenance needs.
Fiber optic connectors have traditionally been the biggest concern in using fiber optic systems. The ideal interconnection of one fiber to another would have two fibers that are optically and physically identical held by a connector or splice that squarely aligns them on their center axes. However, in the real world, system loss due to fiber interconnection is a factor. A connector should align the fibers on their center axes, but when one fiber's axis does not coincide with the other fiber's axis, lateral displacement occurs. A displacement of only 10% of the core axis diameter results in a loss of about 0.5 dB. Since the tiny core of an optical fiber is what transmits the actual light, it is imperative that the fiber be properly aligned with emitters in transmitters, photo-detectors in receivers and adjacent fibers in splices. This is the function of the optical connector. Because of the small sizes of fibers, the optical connector is usually a high precision device with tolerances on the order of fractions of a thousandth of an inch. Accordingly, system integrity is improved and costs are lowered when fiber optic connections and splices are minimized. Splicing is only needed if the cable runs are too long for one straight pull. Making a splice in fiber optic cable is many times more difficult and expensive if it must be made undersea. Accordingly, avoiding splices in fiber optic cable is of particular importance in the undersea environment.
One way of avoiding splices in a fiber optic cable is to place the cable in a conduit that covers the entire distance to be traversed. Couplings are used to join multiple sections of conduit to create a continuous passageway from the source to the destination. A single run of fiber optic cable can then be threaded through the conduit passageway without the need for splices. This technique requires couplings that provide a substantially straight path through the body of the coupling and an absence of features which might cause the cable to “hang up” as it passes through.
Fiber optic cable is often pulled for much longer distances than electrical cable. Continuous fiber pulls of over 4,000 feet are not extraordinary. These long pulls minimize the number of splices in fiber cable, which is desirable for fiber performance. The light weight of the cable makes these long pulls possible, although proper lubrication and a good conduit installation are also necessities. The placement of fiber optic cable in conduit is quite common. Conduit offers protection from crushing, environmental disruption, animals, and other environmental abuse, plus easier replacement or upgrade in the future.
Fiber optic cable can be threaded through a fluid-tight conduit by attaching a ball having a diameter approximately equal to the inner diameter of the conduit to the leading end of the cable. Fluid under pressure may then be pumped through the conduit and the ball acts as a piston within a cylinder (defined by the conduit walls), pulling the fiber optic cable through the conduit. The fluid may be selected or formulated to provide a lubricating action for the cable jacket sliding through the conduit. It will be appreciated that this method requires that sections of conduit be joined with fluid-tight couplings.
Sections of conduit for fiber optic cables, electrical cables and the like need to be joined together in such a way that a straight and smooth passageway through the coupling device results. This is because the cable, fiber or wire must usually be pulled or threaded through the conduit. Any discontinuity on the interior surface of the conduit presents the possibility of a snag. In the undersea environment, there is also a need to prevent marine organisms and debris from entering an open coupling. Conventional conduit couplings do not provide means for sealing the conduit when a coupling is open.
Hydraulic couplings in a variety of configurations are routinely used in off-shore petroleum exploration and production facilities. FIG. 1 is a cross-sectional view of one such coupling of the prior art. The couplings generally consist of a male member and a female member with connecting, sealed, fluid passageways. The female member generally is a cylindrical body with a relatively large diameter longitudinal bore at one end and a relatively small diameter longitudinal bore at the other. The small bore facilitates connections to hydraulic lines, while the large bore seals and slidingly engages the male member of the coupling.
The male member includes a cylindrical body with a probe section approximately equal to the diameter of the female member bore, and a connection at its other end to facilitate connection to hydraulic lines. When the probe section of the male member is inserted into the bore of the female member, according to various embodiments of the device, fluid flow is established between the male and female members.
Although hydraulic lines are most commonly formed of tubular material, the hydraulic couplings of the prior art are unsuited for joining lengths of tubular conduit. As is typical in such hydraulic couplings, both the male and female members have poppet valves which close automatically when the coupling halves are separated in order to keep hydraulic fluid from leaking out and seawater from leaking into the system. The nature of the poppet valves is such that the fluid flow path is not straight through the coupling, but is rather a tortuous path. Such a flow path is acceptable for hydraulic fluid, but unsuitable for a conduit through which a cable must be run. Examples of undersea hydraulic couplings are disclosed in U.S. Pat. No. 4,694,859 and U.S. Pat. No. 6,626,207 and U.S. Pat. No. 6,375,153.
What is needed is a conduit coupling suitable for use in the undersea environment that provides a straight-through passageway and automatic closure of the passageway when the coupling is decoupled. The present invention solves this problem.